Automobiles have multiple control modules that monitor the operation of a vehicle. One function of a control module is to report diagnostic faults. These diagnostic faults are reported to a driver though an indicator light that is typically located on an instrument cluster. When the indicator light is enabled, the driver is notified that the vehicle has experienced a problem and should be serviced soon. Once the vehicle has been serviced, a technician resets the diagnostic faults using a service tool.
Resetting the diagnostic faults with a service tool is the preferred method to clear a fault. However, the diagnostic faults can be reset without a service tool if the code suffers a single point ROM or RAM failure. In the event of a ROM or RAM failure, there is a possibility that the clear diagnostic faults flag may become stuck in one state. This may cause the clear diagnostic faults algorithm to continuously clear all diagnostic faults. This “sleeping fault” is undesirable because the driver would not be notified that diagnostic faults currently exist and no remedial action would be taken. In other words, the operator will not be notified that the vehicle may have a significant problem requiring service and may cause further damage that would otherwise be avoided.